Working With Nature for Better Land and Water Restoration: A Case Study of Organic Pesticide Remediation

Organic Pesticides are chemicals of global concern due to their persistence in the environment, their ability to bio-magnify and bio-accumulate in ecosystems, and the difficulty and cost of recovering these compounds from contaminated soils and groundwater. Treatment of soil frequently requires incineration or hazardous waste land filling, whereas restoration of groundwater has remained elusive. The compounds are almost impossible to physically remove through pump and treat or vacuum extraction technologies and attempts at in-situ destruction, such as chemical oxidation, chemical reduction or in-situ heating, have not provided practical results.

“In the pursuit of long-term remedial solutions, natural subsurface ecosystems may be a more powerful partner than previously understood”

In this NewFields case study we look at a project where the environmental monitoring data, at a pesticide manufacturing facility in the United States, has provided indications that natural subsurface ecosystems may be helping reduce the contaminate concentrations in groundwater with little to no external input.


The site manufactured pesticides until 1965 and fertilizer until the 1980s. Liquid waste streams and off-spec product was disposed in an onsite lagoon of several acres. There was an accumulation of 10 to 12 feet of sludge consisting primarily of lime sulfate, with a mixture of fertilizer manufacture waste and off-spec pesticides. A remedy to excavate, stabilize the sludge with cement, replace the stabilized material, and install a double lined cap over the lagoon was selected in 2008 with a Record of Decision in 2009. Due to delays, however, at present this solution has not been implemented.

The Data

At the time of remedy selection there was only 5 years of dependable time series data in the shallow groundwater around the old lagoon. Due to delays in implementation an additional 12 years of time series data, representing largely undisturbed conditions, became available. Unexpectedly, all of the COCs have decreased in concentration over the intervening years.

Of the 41 COCs identified as requiring remediation at the outset, 13 remain with groundwater concentrations off-site exceeding drinking water standards (See Figure 1). Of those 13, in the immediate vicinity of the source material, six are currently non detect, two are below MCLs, and two are decreasing at a rate that is on track to achieve performance standards within ten years.

The remaining three COCs (two BHC compounds, and chlorobenzene) are displaying a trend indicating the potential for biodegradation of the BHC isomers to chlorobenzene. The pattern of decay is consistent with studies[1] that report the production of chlorobenzene during the anaerobic degradation of BHC isomers[2]. Isolates capable of degrading one or more of the four BHC isomers under anaerobic conditions include: Clostridium rectum,  Clostridium sphenoides, Clostridium butyricum, Clostridium pasteurianum, Citrobacter freundii, Desulfovibrio gigas, Desulfovibrio africanus, Desulfococcus multivorans, and Dehalobacter. This literature also indicates that gamma and alpha isomers are degraded more rapidly than delta and beta. Although decreasing in concentration slower than the other two isomers, beta-BHC, delta-BHC are still declining in the vicinity of the lagoon.

Microbial Induced Calcium-Carbonate Precipitation

The contents of the old lagoon is a factor to be considered in assessing why groundwater may be experiencing declining COC concentrations. The lagoon received waste streams that included calcium (lime sulfur) and nitrogen from the fertilizer manufacture. The calcium and nitrogen source material are prerequisites for microbial induced calcium carbonate precipitation (MICP) a process in which ureolytic bacteria hydrolyze a urea or nitrogen source. This process increases the alkalinity of the pore fluid and induces calcium carbonate precipitation (Fujita et al. 2008[3], Stocks-Fischer et al. 1999[4]). The precipitation of calcium carbonate bonds the soil particles together and increases the density of the soil by decreasing its void ratio (Montoya and DeJong 2015[5]). Most importantly the academic literature indicates MICP can also result in immobilizing trace elements within the material (Fujita et al. 2004[6], Fujita et al. 2010[7], Montoya et al. 2015[8]).

MICP can enhance coal ash and mine tailing stability. It can also minimize the mobility of trace elements within the materials. Bacillus which is a ubiquitous bacteria, eat urea and in the presence of calcium, calcium carbonate precipitant will be produced. Calcium carbonate will grow on the surface of these cells and the coal ash or tailings will be trapped in between these cells thus a solid block of waste will be generated (figure 2).

The time series pattern of decreases in contamination both on- and off-Site is an indication that the rate of natural attenuation exceeds existing contaminant transport from the lagoon. A 3-D representation of lagoon cross-section is shown in figure 3, which includes the positioning of the various subsurface layers and the waste material.

The data currently does not exist to establish what combination of factors are contributing to the observed attenuation. There are multiple factors that could be contributing:

  • low permeability soils below the sludges;
  • MICP;
  • microbial dechlorination;
  • and/or simple dilution.

However, the empirical results suggest that the subsurface ecosystem could be a powerful, highly sustainable and resilient ally in achieving long term protection of the groundwater and recipients.

The principal challenge in exploiting and enhancing inherently resilient functioning ecosystem processes, is the different standard of proof between an active engineered solution and a nature-based solution. The planned remedy is expected, by the designers and the regulators, to worsen groundwater conditions in the short term; critically there is NO agreement or even verifiable prediction of how long ‘short-term’ may be. Similar sites that are analog models, including one of the largest pesticide sites in the world, Rocky Mountain Arsenal in Colorado, indicate that source stabilization and associated pump and treat is unlikely to return groundwater to performance standards within decades, if ever. Existing natural processes by contrast, at least at this example site, are demonstrably improving groundwater contaminant levels.

Efforts to better understand the natural processes are just beginning and the results will be shared as they become available.


[1] Biochemistry of Microbial Degradation of Hexachlorocyclohexane and Prospects for Bioremediation (Lal, Panday et. al., 2010)

[2] Lal, Panday et. al., 2010. Biochemistry of Microbial Degradation of Hexachlorocyclohexane and Prospects for Bioremediation, Microbiology and Molecular Biology Reviews

[3] Fujita, Y., Taylor, J. L., Gresham, T. L., Delwiche, M. E., Colwell, F. S., McLing, T. L, & Smith, R. W. (2008). Stimulation of microbial urea hydrolysis in groundwater to enhance calcite precipitation. Environmental science & technology, 42(8), 3025-3032 3. Soil Biology and Biochemistry, 31(11), 1563-1571.

[4] Stocks-Fischer, S., Galinat, J. K., & Bang, S. S. (1999). Microbiological precipitation of CaCO

[5] Montoya, B. M., & DeJong, J. T. (2015). Stress-strain behavior of sands cemented by microbiallyi induced calcite precipitation. Journal of Geotechnical and Geoenvironmental Engineering, 141(6), 04015019.

[6]Fujita, Y., Redden, G. D., Ingram, J. C., Cortez, M. M., Ferris, F. G., & Smith, R. W. (2004). strontium incorporation into calcite generated by bacterial ureolysis. Geochimica et Cosmochimica Acta, 68(15), 3261-3270

[7] Fujita, Y., Taylor, J. L., Wendt, L. M., Reed, D. W., & Smith, R. W. (2010). Evaluating the potential of native ureolytic microbes to remediate a 90Sr contaminated environment. Environmental science & technology, 44(19), 7652-7658.

[8] Montoya, B. M., & DeJong, J. T. (2015). Stress-strain behavior of sands cemented by microbiallyi induced calcite precipitation. Journal of Geotechnical and Geoenvironmental Engineering, 141(6), 04015019.

About the Author

Mr. William “Billy” Hall, P.E. is the Chairman of the Board of NewFields, an environmental, engineering, and construction management consulting firm that provides our clients with practical and strategic solutions. Mr. Hall co-founded NewFields in 1995 as an alternative to the large, institutional consulting firms and served as Chief Executive Officer until 2015. Mr. Hall is responsible for helping to develop and implement the company’s strategic vision while he maintains a robust technical practice.  He has over 40 years of experience managing multidisciplinary environmental projects with expertise ranging from data and environmental systems analysis and design to civil design and construction management.

Richard J. Williams PhD is a highly qualified Environmental Geologist and project manager with 10 years of experience in environmental management, data processing and interpretation, site management and contract management, His expertise is in geological interpretation, contaminated land and groundwater assessment projects, project co-ordination, permitting and database management. He has been responsible for the management of multimillion pound remediation projects in the UK and is the head of the UK office.